Field of the Invention
The invention is directed to a non-volatile memory and more particularly, to a resistive random access memory.
Description of Related Art
A resistive random access memory (RRAM) is a type of a non-volatile memory. The resistive random access memory having advantages, such as low writing operation voltage, short write and erase time, long retention time, non-destructive reading, multi-level capability, simple structure and small cell area, has a great application potential in future personal computers and electronic equipment and thus, is being widely developed.
Generally, a resistive random access memory is a metal-insulating layer-metal (MIM) structure composed of a top electrode, a bottom electrode and a resistance changeable layer therebetween.
When a positive bias is applied to the resistance changeable layer, oxygen ions are attracted by the positive bias to leave the resistance changeable layer, such that oxygen vacancy is generated, a filament structure is formed, and the filament structure is in a conductive states, and as a result, the resistance changeable layer is converted from a high-resistance state (HRS) to a low-resistance state (LRS). Typically, a titanium (Ti) layer is disposed between the top electrode and the resistance changeable layer to store oxygen ions leaving the resistance changeable layer due to the attraction of the positive bias.
When a negative bias is applied to the resistance changeable layer, the oxygen ions return to the resistance changeable layer, such that a conductive filament is broken and is in a non-conductive state, and the resistance changeable layer is converted from the LRS to the HRS. However, if the oxygen ions have diffused out in the Ti layer, an issue of incomplete reset operation will occur.